Photoresists and photoresist films are utilized in the manufacture of highly integrated semiconductors such as integrated circuits (ICs), Printed Circuit Boards (PCBs) and electronic display devices such as Cathode Ray Tubes (CRTs), color liquid crystal displays (LCDs) and organic electroluminescent displays (ELs or ELDs). The manufacturing processes for these devices use photolithography and photofabrication techniques. The photoresist films require a resolution sufficient to form a pattern with extremely fine lines and small space area not more than 7 μm.
The physical properties of photoresists can vary in such characteristics as solubility in a certain solvents, coloration, curing and the like via chemical modification of the molecular structure of the photoresist resin or the photoresist.
In recent years, processes for manufacturing TFT-LCDs using liquid photoresist compositions have become increasingly complicated and difficult as substrate sizes are increasing and the problems associated with liquid photoresist compositions have become more marked. Positive liquid photoresists exhibit problems such as reduced resolution and sensitivity due to sedimentation during storage, inferior pattern design due to residues on a coated surface, etc. Therefore, there exists a need to develop novel photoresists to solve such problems.
The desire for positive dry resist technology arose from the disadvantages associated with conventional liquid positive photoresists. These disadvantages led to elevated process costs. For example, spin coating a photoresist onto a semiconductor wafer results in losses of expensive photoresist material. The machinery for spin coating resists represents a substantial capital expense, and the time and management associated with spin coating results in additional process expense. The filtration associated with point-of-use application of photoresists is also cost-intensive. The wastage of photoresists at all points in the spin coating process also represents a substantial part of the photoresist cost. Also, positive liquid photoresist compositions generate insoluble materials (that is, undergoes sedimentation) during storage, leading to reduction of resolution and sensitivity. As a result, a practical dry film positive photoresist technology becomes highly desirable.
Conventional dry film photoresist technology began development during the 1960's when liquid negative photoresists were adapted to dry film technology for the manufacture of large featured, low resolution devices such as printed circuit board (PCB) patterns. However, the poor resolution of these negative dry film resists inhibited the application of dry film technology to high resolution applications such as ICs, LCDs etc.
Positive dry film resists first emerged during the 1980's, where technologies developed that exploited the properties of thermoplastic resins. For example, cellulose resins were utilized as the basis of dry film positive resists (U.S. Pat. No. 5,981,135). Additional dry film positive resists were developed by DuPont (U.S. Pat. No. 4,193,797 and U.S. Pat. No. 5,077,174), which were based upon acrylate or methacrylate resins. These related art thermoplastic positive dry film photoresists thus shared the disadvantages of the negative resists because utilizing cellulosic or acrylic resins yield a thick dry film photoresist that has low resolution.
As a result, application of these related art dry film in positive photoresists has proven problematic in regards to the thin films required for advanced semiconductor manufacturing applications. That is, as the photoresist layer widths necessarily become thinner for high resolution photolithography, the requirement for a uniform thin film increases. For example, a thin film of photoresist is more sensitive to external phenomena such as substrate roughness. A sufficiently non-uniform substrate can cause defects in the photoresist layer such as “fish eye”.
Consequently, there is a strong need for improved photoresist films that overcome various problems such as thickness deviation of the coating layer, smoothness, distortion, coagulation, foaming, coating loss and the like, which are caused during necessary processes such as spin-coating or similar processes when forming micro patterns on LCDs, organic ELDs and the like when using conventional liquid positive type photoresist compositions. The improved photoresist films should also exhibit high resolution, excellent line width controllability, high thermal resistance, high sensitivity, improved film residual rate, high dry etching resistance and high development properties, and be applicable to micro-fine processing of LCDs, organic ELDs and the like.